Polymerization of butadiene-1,3



Patented Jan. 2, 1945 2.36am ronmarza'r'ron or sarcomas-1.:

. Charles F. Fryling, Silver Lake, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application November 2, 1940, Serlal No. 364,101

14 Claims.

This invention relates to the polymerization of butadienes-l,3, and particularly to a method whereby butadienes-1,3 may be polymerized in an aqueous emulsion to form products closely resembling natural crude ,rubber.

The emulsion polymerization of butadienes-1,3 either alone or in admixture with other conjugated dienes or other materials copolymerizable therewith to form compositions of matter more or less resembling rubber is well known. It has been commonly observed. however, that the products of such polymerization often resemble vulcanized rubber rather than natural crude rubber in respect to solubility, plasticity, and processing characteristics. Thus, it has often been found that the polymers were insoluble in, and in some cases, not even swelled by benzene or acetone, and that they were tough, non-plastic materials which either would not homogenizc on a millor which were very diflicult to mill and'subject to other ordinary processing operations for natural rubber.

I have now discovered a class of materials which modifies the emulsion polymerization of butadienes-1,3 in such a manner that polymers more nearly resembling natural crude rubber may be produced than when the polymerization is carried on in the absence of the'materials of this invention. This class of materials, which I have termed modifiers, consists of nitrodiaryl polysulfides, by which is meant diaryl polysulfldes containing a nitro substituent on at least one of the aromatic nuclei. The preferred class of materials consists of compounds having the structural formula NOa-RrAx-Ra-NO:

substituents are also included in the broad scope of the invention, although the di-p-nitroaryl disulfides are at present the preferred materials.

The invention may be better understood from the following'speciflc examples which are to be regarded as merely illustrating preferred embodiments and not as limiting the invention in any respect.

Example I--7.5 gm. of butadiene and 2.5 gm. of acrylonitrile were sealed in a glass polymerization tube with 25 cc. of a 2% aqueous solution of palmitic acid which had been 85% neutralized with sodium hydroxide, 1 cc. of hydrogen peroxide, and 0.058 g. of di-p-nitrophenyl disulfide, and polymerized by agitating the contents of the tube at C. The copolymer appeared either to dissolve completely or'swell infinitely in benzene, and to be coherent on a mill. A similar copolymer prepared in the absence of the di-pnitrophenyl disulfide was insoluble in and onlyslightly swelled by benzene, and had a tendency to crumble on the mill rather than to form a co-.

herent mass. It was also found that when the copolymer prepared in the presence of di-pnitrophenyl disulfide was vulcanized according to a standard test recipe, the vulcanizate had an ultimate tensile strength of 5650 lbs/in. and an'elongation at break of 570%, while the vulcanized copolymer prepared in the absence of any modifier possessed an ultimate tensile strength of 4550 lbs/in. and an elongation at break of 510%.

Example II7.5 gm. of butadlene and 2.5 gm. of acrylonitrile were sealed in a glass polymerization tube with 25 cc. of a 2% aqueous solution 01' myristic acid which had been 85% neutralized with sodium hydroxide, 1 cc. of hydrogen peroxide, and 0.04 gm. of di-p-nitrophenyl disulflde, and polymerized by agitating the contents 7 of the tube at 30 C. The copolymer was a plastic, coherent material which was 57% soluble in benzene and could be easily milled, while repetition of the experiment with the omission of the dip-nitrophenyl dlsulilde yielded a non-coherent, non-plastic copolymer which was only 5% soluble in benzene and could, be milled only with difllculty. elongation at break of the vulcanized modified copolymer averaged 5300 lbs/in. and 620% respectively, while the corresponding values for the vulcanized unmodified copolymer were 3700 lbs/in. and 360%. 1

Example III-when di-o-nitrophenyl disulfide was substituted for the di-p-nitrophenyl disulflde in Example 11, a very plastic coploymer was produced which was 20% soluble in benzene andformed a vulcanizate having an ultimate tensile-strength averaging 5300 lbs/in. and an elongation at break averaging 740 lbs/in.

While the above examples are confined to the use of di-nitrophenyl disulfldes as the modifiers, it will be clear to those skilled in the art that portion in which the modifier is included in the composition depends somewhat upon the properties desired in the copolymer, the higher proportions of modifier in general producing softer, more soluble polymers. Very small amounts of modifier such as 0.1% based on the monomer or The ultimate tensile strength and 'which serves to prevent or inhibit cross-linkage,

the products of emulsion polymerizations which have been carried to completion contain numerous cross-linkages which affect the properties of the polymer in much the same manner as the cross-linkages formed during the vulcanization of natural crude rublkr by sulfur change the properties of the crude rubber. This theory explains why the polymers prepared in the presence. of modifying agents are in general more plastic and more soluble than unmodified polythere. This theory is presented only by way of explanation and is not intended as a limitation on the invention, for regardless of the correctnessof the theory, the inclusion of a nitrodiaryl disulflde in emulsion polymerization batches pro duces the beneficial results hereinbefore described. I

The modifying agents of this invention may be employed in emulsion polymerizations of butadienes-1,3 such as butadiene-1,3 itself commonly called butadlene) as well as 2,3-dimethylbutadiene, isoprene, 2-chlorobutadiene, and piperylene, either alone or in admixture with each other or with comonomers polymerizable therewith such as styrene, acrylonitrile, methyl methacrylate, vinyl acetate, vinylidene chloride, methyl vinyl ketone, methyl vinyl ether, and other polymerizable hydrocarbons,'nitriles, esters, ketones, and others. These comonomers are preferably, though not necessarily employed in minor proportions.

The polymerization of the above materials in aqueous emulsion may be efiected by various catalysts such as per-compounds including hy= drogen peroxide, ammonium persulfate, potassium persulfate, and other peroxides, persulfates,

perborates, percarbonates, and the like, diazoaminobenzene, and dipotassium diazomethane disulfonate. Since the modifying agents of this invention have an inhibiting action, it may be de sirable to include an activator for the catalyst in the emulsion, particularly when large amounts of modifying agent are employed. When hydrogen peroxide is being employedas the catalyst,

for instance, compounds which may form comp'lexes with the hydrogen peroxide such as sodium pyrophosphate, sodium oxalate, potassium fluoride, urea, glycine, alanine, and the like may be employed to activate the catalyst and produce a v desirable type of polymer in a shorter period of time.

Any of the ordinary emulsifying agents such as fatty acid soaps, hymolal sulfates or sulfonates, alkylated aromatic salts of high molecular weight, organic bases, etc. may be employed to effect the emulsion of the monomers in the water. When the modifiers of this invention are employed in high proportions, the consequent inhibition of the rate of polymerization may be counter-balanced assesses by employing emulsifying agents which are at the same time polymerization catalysts, such as fatty acid soaps, and by using somewhat higher proportions than are necessary to form good emulsions.

Although I have herein disclosed specific embodiments of my invention, I do not intend to limit the invention solely thereto, for it will be obvious to those skilled in the art that many variations and modifications are within the spirit and scope of the invention as defined in the appended claims.

I claim:

1. The method which comprises polymerizing an aqueous emulsion of a polymerizable butadiene-l,3 in the presence of a nitrodiaryl polysulfide.

2. The method which comprises polymerizing an aqueous emulsion of a polymerizable butadione-1,3 in the presence of a nitrodiaryl disulfide.

3. The method which comprises polymerizing an aqueous emulsion of a polymerizable butadiene-1,3 in the presence of a compound having the structural formula wherein R1 and R2 are arylene groups and X is a small integer greater than 1.

'7. The method'which comprises polymerizing an aqueous emulsion of a mixture of butadiene- 1,3 and a minor proportion of acrylonitrile in the presence of a compound having the structural formula wherein R1 and R2 are arylen groups.

8. The method which comprises polymerizing an aqueous emulsion of butadiene-l,3 in the presence of a compound having the structural formula wherein R1 and R2 are phenylene groups and X is a small integer greater than 1.

9. The method which comprises polymerizing an aqueous emulsion of a mixture of butadiene- 1,3 and a minor proportion of acrylonitrile in the presence of di-p-nitrophenyl disulfide.

10. A composition of matter prepared by the method of claim 1.

11. A composition of matter prepared by the method of claim 3.

12. A composition of matter prepared by th method of claim 7.

13. A composition of matter prepared by the method of claim 8.

14. A composition of matter prepared by the method of claim 9.

CHARLES F. ERYLING. 

